First break picking for full wavefield travel-time inversion

Abstract

A method for picking first breaks on a synthetic seismic dataset for a full wavefield travel-time inversion is provided. This method includes obtaining a synthetic seismic dataset and for each synthetic trace, determining a plurality of synthetic trace amplitude maxima and minima, determining a modified energy ratio trace, and forming a trace mask based at least in part, on an amplitude of the synthetic trace and on an amplitude of the modified energy ratio trace. The method further includes determining for each synthetic trace, a positive estimated first break based on the plurality of synthetic trace amplitude maxima and the trace mask and a negative estimated first bread based on the plurality of synthetic trace amplitude minima and the trace mask. The method concludes with determining a predicted first break for each synthetic trace from the positive estimate first break and the negative estimate first break.

What is claimed is: 
     
       1. A method, comprising:
 obtaining, using a computer processor, a synthetic seismic dataset for a subterranean region of interest, wherein the synthetic seismic dataset comprises a plurality of synthetic traces; 
 determining, using the computer processor, for each synthetic trace of the plurality of synthetic traces, a plurality of synthetic trace amplitude maxima and a plurality of synthetic trace amplitude minima; 
 determining, using the computer processor, a modified energy ratio trace from said each synthetic trace, wherein each sample of the modified energy ratio trace comprises the ratio of a first energy within a first time window of the synthetic trace after the sample to a second energy within a second time window of the synthetic trace before the sample; 
 forming, using the computer processor, for said each synthetic trace, a trace mask based, at least in part, on an amplitude of the synthetic trace and on an amplitude of the modified energy ratio trace; 
 determining, using the computer processor, for said each synthetic trace:
 a positive estimated first break based, at least in part, on the plurality of synthetic trace amplitude maxima and the trace mask, and 
 a negative estimated first break based, at least in part, on the plurality of synthetic trace amplitude minima and the trace mask; and 
 
 determining, using the computer processor, for said each synthetic trace, a predicted first break from the positive estimate first break and the negative estimate first break. 
 
     
     
       2. The method of  claim 1 , further comprising:
 obtaining an observed seismic dataset comprising a plurality of observed traces; 
 determining an observed first break for each of the plurality of observed traces; 
 forming an objective function based, at least in part, on a difference between the observed first break for each of the plurality of observed traces and the predicted first break for each of the plurality of synthetic traces; and 
 determining a seismic velocity model based, at least in part, on an extremum of the objective function. 
 
     
     
       3. The method of  claim 2 , further comprising:
 forming an image of the subterranean region of interest based, at least in part, on the seismic velocity model and the observed seismic dataset. 
 
     
     
       4. The method of  claim 1 , wherein obtaining the synthetic seismic dataset comprises:
 obtaining an initial seismic velocity model of the subterranean region of interest and a geometry of seismic sources and seismic receivers; and 
 determining the plurality of synthetic traces based on a solution to a wave equation. 
 
     
     
       5. The method of  claim 1 , wherein forming, for said each synthetic trace, a trace mask, comprises:
 determining a first mask based, at least in part, on a scaled synthetic trace amplitude and a first predetermined threshold; 
 determining a second mask based, at least in part, a modified energy ratio trace and a second predetermined threshold; and 
 determining a third mask by forming a product of the first mask and the second mask. 
 
     
     
       6. The method of  claim 1 , wherein selecting for said each synthetic trace, the positive estimated first break comprises:
 determining a positive first mask based, at least in part, on a scaled positive-valued synthetic trace amplitude having a greater absolute value than a first predetermined threshold; and 
 determining a plurality of candidate positive first breaks for said each synthetic trace based, at least in part, on the plurality of synthetic trace maxima and a positive third mask. 
 
     
     
       7. The method of  claim 1 , wherein selecting for said each synthetic trace, the positive estimated first break further comprises:
 sorting seismic receivers in order of increasing distance from a seismic source;
 selecting an earliest candidate positive first break as the positive estimate first break of the synthetic trace for a nearest receiver to the seismic source; and 
 selecting, for each of the sorted receivers in order of increasing distance from the seismic source, a positive estimated first break, wherein the positive estimated first break is chosen to be a candidate positive first break closest in time to the positive estimated first break of a preceding synthetic trace. 
 
 
     
     
       8. The method of  claim 1 , wherein selecting for said each synthetic trace, a negative estimated first break comprises:
 determining a negative first mask based, at least in part, on a scaled negative-valued synthetic trace amplitude having a greater absolute value than a first predetermined threshold; and 
 determining a negative estimated first break of said each synthetic trace based, at least in part, on the plurality of synthetic trace minima and the negative first mask. 
 
     
     
       9. The method of  claim 7 , wherein selecting for said each synthetic trace, the negative estimated first break further comprises:
 sorting seismic receivers in order of increasing distance from the seismic source; 
 selecting an earliest candidate negative first break as the negative estimated first break of the synthetic trace for the nearest receiver to the seismic source; and 
 selecting, for each of the sorted receivers in order of increasing distance from the seismic source, a negative estimated first break, wherein the negative estimated first break is chosen to be a candidate negative first break closest in time to the negative estimated first break for the preceding synthetic trace. 
 
     
     
       10. The method of  claim 1 , wherein determining, for said each synthetic trace, the predicted first break comprises selecting the earlier of the positive estimated first break and the negative estimated first break. 
     
     
       11. A non-transitory computer readable medium storing instructions executable by a computer processor, the instructions comprising functionality for:
 obtaining, using a computer processor, a synthetic seismic dataset for a subterranean region of interest, wherein the synthetic seismic dataset comprises a plurality of synthetic traces; 
 determining, using the computer processor, for each synthetic trace of the plurality of synthetic traces, a plurality of synthetic trace amplitude maxima and a plurality of synthetic trace amplitude minima; 
 determining, using the computer processor, a modified energy ratio trace from said each synthetic trace, wherein each sample of the modified energy ratio trace comprises the ratio of a first energy within a first time window of the synthetic trace after the sample to a second energy within a second time window of the synthetic trace before the sample; 
 forming, using the computer processor, for said each synthetic trace, a trace mask based, at least in part, on an amplitude of the synthetic trace and on an amplitude of the energy ratio trace; 
 determining, using the computer processor, for said each synthetic trace:
 a positive estimated first break based, at least in part, on the plurality of synthetic trace amplitude maxima and the trace mask, and 
 a negative estimated first break based, at least in part, on the plurality of synthetic trace amplitude minima and the trace mask; and 
 
 determining, using the computer processor, for said each synthetic trace, a predicted first break from the positive estimate first break and the negative estimate first break. 
 
     
     
       12. The non-transitory computer readable medium of  claim 11 , further comprising:
 obtaining an observed seismic dataset comprising a plurality of observed traces; 
 determining an observed first break for each of the plurality of observed traces; 
 forming an objective function based, at least in part, on a difference between the observed first break for each of the plurality of observed traces and the predicted first break for each of the plurality of synthetic traces; and 
 determining a seismic velocity model based, at least in part, on an extremum of the objective function. 
 
     
     
       13. The non-transitory computer readable medium of  claim 12 , further comprising:
 forming an image of the subterranean region of interest based, at least in part, on the seismic velocity model and the observed seismic dataset. 
 
     
     
       14. The non-transitory computer readable medium of  claim 11 , wherein obtaining the synthetic seismic dataset comprises:
 obtaining an initial seismic velocity model of the subterranean region of interest and a geometry of seismic sources and seismic receivers; and 
 determining the plurality of synthetic traces based on a solution to a wave equation. 
 
     
     
       15. The non-transitory computer readable medium of  claim 11 , wherein forming, for said each synthetic trace, a trace mask, comprises:
 determining a first mask based, at least in part, on a scaled synthetic trace amplitude and a first predetermined threshold; 
 determining a second mask based, at least in part, an energy ratio and a second predetermined threshold; and 
 determining a third mask by forming a product of the first mask and the second mask. 
 
     
     
       16. The non-transitory computer readable medium of  claim 11 , wherein selecting for said each synthetic trace, the positive estimated first break comprises:
 determining a positive first mask based, at least in part, on a scaled positive-valued synthetic trace amplitude having a greater absolute value than a first predetermined threshold; and 
 determining a plurality of candidate positive first breaks for said each synthetic trace based, at least in part, on the plurality of synthetic trace maxima and a positive third mask. 
 
     
     
       17. The non-transitory computer readable medium of  claim 11 , wherein selecting for said each synthetic trace, the positive estimated first break further comprises:
 sorting seismic receivers in order of increasing distance from a seismic source; 
 selecting an earliest candidate positive first break as the positive estimate first break of the synthetic trace for a nearest receiver to the seismic source; and 
 selecting, for each of the sorted receivers in order of increasing distance from the seismic source, a positive estimated first break, wherein the positive estimated first break is chosen to be a candidate positive first break closest in time to the positive estimated first break of a preceding synthetic trace. 
 
     
     
       18. The non-transitory computer readable medium of  claim 11 , wherein selecting for said each synthetic trace, a negative estimated first break comprises:
 determining a negative first mask based, at least in part, on a scaled negative-valued synthetic trace amplitude having a greater absolute value than a first predetermined threshold; and 
 determining a negative estimated first break of said each synthetic trace based, at least in part, on the plurality of synthetic trace minima and the negative first mask. 
 
     
     
       19. The non-transitory computer readable medium of  claim 17 , wherein selecting for said each synthetic trace, the negative estimated first break further comprises:
 sorting seismic receivers in order of increasing distance from the seismic source; 
 selecting an earliest candidate negative first break as the negative estimated first break of the synthetic trace for the nearest receiver to the seismic source; and 
 selecting, for each of the sorted receivers in order of increasing distance from the seismic source, a negative estimated first break, wherein the negative estimated first break is chosen to be a candidate negative first break closest in time to the negative estimated first break for the preceding synthetic trace. 
 
     
     
       20. The non-transitory computer readable medium of  claim 11 , wherein determining, for said each synthetic trace, the predicted first break comprises selecting the earlier of the positive estimated first break and the negative estimated first break.